Studies will be undertaken to examine the role of T lymphocytes in controlling the changes in antibody affinity which occur following immunization. Both the effects of helper and suppressor T cells on antibody affinity will be investigated. In addition, the effects of T-cell tolerance and suppressor T-cell mediated tolerance on antibody affinity will be studied. Finally, we will study the ontogeny of the capacity of the B cell population to produce a heterogeneous response to T independent antigens and compare the maturation of this function with the maturation of the capacity to produce a heterogeneous response to T dependent antigens which we have studied previously.